1. Field
The present embodiments relate to an organic light emitting display device, and more particularly, to an organic light emitting display device including an electron injection layer (EIL).
2. Description of the Related Technology
Organic light emitting display devices use a material that emits light when a voltage is applied. In comparison to liquid crystal display devices, organic light emitting display devices may have a higher luminance, wider viewing angles, and faster response speeds and may have a smaller thickness because a backlight is not required.
In an organic light emitting display device, an organic emission layer (EML) is interposed between an anode and a cathode. If a voltage is applied between the electrodes, holes from the anode and electrons from the cathode are injected into the organic EML. The injected holes and electrons cause electron switches between neighboring molecules in the organic EML and move to opposite electrodes. If the electrons and holes are recombined in some molecules, molecule excitons in an excited state of high energy are formed. The molecule excitons return to a ground state of low energy while emitting unique light of a material. This is an emission mechanism of the organic light emitting display device.
In order to improve the emission efficiency of an organic light emitting display device, efficient extraction of holes and electrons from an anode and a cathode and efficient transportation of holes and electrons to an EML are important. For this, a structure in which p-type and n-type organic semiconductor layers are stacked on an organic EML is generally used. Representative layers in the stacked structure include a hole injection layer (HIL) for receiving and transporting holes injected from an anode, a hole transport layer (HTL) for transporting the injected holes to an EML, an electron injection layer (EIL) for receiving and transporting electrons injected from a cathode, an electron transport layer (ETL) for transporting the injected electrons to an EML, and an EML for emitting light by recombining holes and electrons. The stacked structure of organic layers may increase the emission efficiency and may reduce a driving voltage.
Also, in an organic light emitting display device using microcavities, a stacked structure has a thickness that varies according to red (R), green (G), and blue (B) colors, and generally includes ten or more stacked layers. Due to the variance in thickness according to R, G, and B colors and the large number of stacked layers, a deposition structure and deposition equipment are complicated. Also, currently, a cathode of an organic light emitting display device is formed of only Mg:Ag. However, in a large display device, Mg:Ag causes a voltage drop due to its high resistance (˜40 ohm/sq) and thus a problem in viewing angle occurs. Also, since the transmittance of Mg:Ag is reduced toward a long wavelength, a correction in viewing angle is required.